(a) Field of the Invention
The present invention relates to an image data decoder for still and moving picture data and, more particularly, to an image data decoder capable of decoding compressed moving picture data and the compressed still picture data with a simplified circuit structure.
(b) Description of the Related Art
Image data decoders are known which is capable of outputting moving picture data to a display unit in real time while decoding compressed moving picture data input therein. Some of these image data decoders have a function for decoding a single macro block line data, or data displayed on sixteen scanning lines, within sixteen line-times in a single image frame. The term xe2x80x9cline-timexe2x80x9d as used herein means a time length required for forwarding or receiving data for a single scanning line.
FIG. 1 schematically shows a conventional image data decoder of the type as mentioned above. The moving picture decoder includes a MPEG (Moving Picture Experts Group) decoder 30 for decoding compressed moving picture data by using a MPEG scheme generally used as an international standard, a decoder control block 31 for controlling the operation of the MPEG decoder 30, and a buffer for outputting the decoded data while temporarily storing the decoded data. The MPEG decoder 30 includes a data latch section 33 and a data processing section 34.
In general, each picture layer constituting a single frame includes a plurality of pixel data and parameters called xe2x80x9cheaderxe2x80x9d attached to each layer constituting the pixel data. The data latch section 33 latches specified parameters from among the parameters included in each layer of the compressed image data input to the MPEG decoder 30. The data processing section 34 forwards the specified parameters to the data latch section 33, starts for decoding the compressed image data input therein for a single frame picture after the decoder control block 31 delivers a start signal to the MPEG decoder 30 for indicating the decode of the moving picture data, whereby the decoded moving picture data are delivered to the buffer 32. The buffer 32 receives the decoded moving picture data from the data processing section 34 to deliver output image data to a display unit not shown.
The decoder control block 31 receives a video synchronizing signal for representing an absolute location on the screen of the display unit, which iterates digits between 0 and 524 in a NTSC standard, a multification factor for effecting enlargement or reduction of the image on the screen based thereon, and location data for specifying the image location on the screen. The decoder control block 31 delivers a decode start signal to the MPEG decoder 30 for indicating the decode of the moving picture data based on the video synchronizing signal, whereas the MPEG decoder 30 delivers a notification signal for notifying the end of the decode after the decode of the moving picture data is finished by the MPEG decoder 30.
The data storage section 33 latches the specified parameters from the moving picture data through the data processing section 34, and the decoder control block 31 receives the multification data and the image location data to deliver the decode start signal to the MPEG decoder 30 in synchrony with the video synchronizing signal. The MPEG decoder 30 responds to the decode start signal to start for decoding the input frame picture corresponding to the parameters latched by the data latch section 33, and delivers the decoded moving picture data to the buffer 32. The buffer 32 outputs the received moving picture data to the display unit while temporarily storing the same.
FIG. 2 shows a timing chart for decoding operation by the conventional MPEG decoder of FIG. 1. Fields which constitute a single frame include an odd-numbered field and an even-numbered field occurring alternately with each other, between which a blanking period is provided. The compressed moving picture data includes a series of frame pictures pic0 to pic3, which sandwich between each two of them a decode stop period Ds0 to Ds3. The image data pic0-top to pic3-top for the odd-numbered fields and the image data pic0-bottom to pic3-bottom for the even-numbered fields are delivered corresponding to the frame pictures pic0 to pic3 as the decoded moving picture data.
In the conventional MPEG decoder, if still picture data, such as a TV program list, is to be displayed on a display unit together with the moving picture data, an additional decoder must be provided for decoding the still picture data separately from the MPEG decoder decoding the moving picture data. The additional decoder increases the circuit scale and the chip size of the MPEG decoder, however. Thus, an image data decoder is desired wherein the decode of the still picture does not substantially increases the circuit scale and the chip size of the image data decoder.
In view of the above, it is an object of the present invention to provide an image data decoder which is capable of decoding still picture data together with moving picture data for enabling display of a still picture and a moving picture on a single display unit, substantially without increasing the circuit scale and the chip size of the MPEG decoder.
The present invention provides a MPEG decoder comprising: a decoding block including a data processing section for decoding moving picture data and still picture data alternately with each other, the moving picture data including a plurality of frame pictures each having a frame period, each adjacent two of the frame pictures being supplied with a first time space therebetween: and a decoder control block including a calculation section for calculating a first time length necessary for said decoding block to decode data for each of the frame pictures and calculating a second time space by subtracting the first time length from the frame period, and a control section for controlling said decoding block to decode the moving picture data for the first time length and to decode the still picture data for a sum of the first time space and the second time space.
In accordance with the image data decoder of the present invention, the single data processing section decodes the moving picture data and the still picture data without an additional processor, thereby reducing the circuit scale of the decoder for decoding moving picture data and the still picture data. If the moving picture data is for TV broadcasting, the still picture data may be preferably for a program list of the TV broadcasting.
The inventors noticed the time length of the time space between frame periods in the conventional image data decoder and the time length of the frame period, and considered that the combination of short time spaces between macro block lines in the frame period and the time space between the frame periods would provide a time length sufficient for decoding at least a part of still picture data.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.